1. Field of the Invention
The present invention relates to a stock unit for storing carriers which are themselves used for storing semiconductor wafers or the like.
2. Description of the Related Art
Stock units for storing carriers each of which holds a plurality of wafers, are used in factories where semiconductor devices are manufactured. The stock units are installed between the places where the wafers undergo various processes, and are used to store temporarily the carriers each holding wafers and also to protect the wafers from accidental damage.
The stock units hitherto known and used are so-called "single-port units". Each of them has only one port through which carriers are inserted into, and pulled out of, the stock unit, either manually or by means of industrial robots. The workers, who are going to insert or pull the carrier from the stock unit, may interfere with each other. Further, it is possible that the robots and/or workers interfere with each other. To prevent an accident of this type, the robot must be strictly controlled. In addition, stockers storing the carriers and the places or environments where the carriers are temporarily located must be kept as clean as possible, using filters, since the carriers store semiconductor wafers. However, the filters are restricted in their fitting positions on the stocker units, even with the single-port units. It is, therefore, more difficult to design a multi-port stock unit which has more than one port.
The conventional stock units have been made in accordance with the customers' specifications. This is because, on which side the stock port should have the port depends on where in the factory the stock unit is installed. They cannot be manufactured in large quantities.